The present invention relates to conveyor systems and more particularly pertains to systems wherein a magnetic proximity system is used to control the operation of a plurality of self-propelled vehicles mounted for travel on a common track.
Those concerned with the development of conveyor systems that employ self-propelled vehicles riding on a common track have long recognized the need for improvements in control means for regulating the driving power of the vehicles. In general, typical vehicles employed in such conveyor systems are propelled by a self-contained electric motor that draws electric power from a pair of electric rails that run adjacent the track or other surface on which the vehicles ride. Because the vehicles cannot pass one another while on the track, some provision is generally made for regulating the speed of the electric motors in the trailing vehicles when they encounter a leading vehicle.
One example of a conveyor system in which motor vehicle speed is regulated is disclosed in U.S. Pat. No. 3,823,673. In the '673 patent, electrical contacts are provided on the front and back surfaces of the vehicles. When a trailing vehicle in the '673 patent bumps into the back end of a leading vehicle that is either stopped or slowly moving, the back contact on the leading vehicle will make electrical contact with the front contact on the trailing vehicle. This contact will be detected by circuitry in the trailing vehicle which in turn will cut off power to the self-contained motor. When contact ceases between the trailing and leading vehicles in the '673 patent, the circuitry in the trailing vehicle will detect this condition and first energize a timing device. After a predetermined time period, the circuitry will then restore power to the motor in the trailing vehicle causing that vehicle to resume its normal speed.
While the device in the '673 patent and in other similar systems have served the general purpose of maintaining reasonably efficient flow of vehicle traffic, they have not proved entirely satisfactory under all conditions of service. For example, in the '673 patent, actual contact between the tandem vehicles is necessary before power to the motor is cutoff in the trailing vehicle. Additionally, in the '673 patent, power is restored to the trailing vehicle after a predetermined time period regardless of the proximity of the leading vehicle. As such, an unsatisfactory amount of vehicle bumping and inefficiencies have been experienced which is significantly reduced in the present invention.